(1) Field of the Invention
The present invention relates to a thermal printer and, more particularly, to a thermal printer arranged to perform recording on two sheets of (copying) paper superposed one on another.
(2) Description of the Related Art
Ordinary thermal printers have a construction such as that shown in FIG. 3, in which a platen 2 in the form a lengthwise flat plate is disposed substantially at a center between front and rear sides of a frame 1 so as to extend to left and right sides of the frame 1 and so that its printing surface is substantially vertical, and in which a carriage shaft 3 is disposed so as to extend parallel to the platen 2 below the front surface of the platen 2 and in the frame 1.
A flange-like guide portion 4 is formed as a front end edge of the frame 1, and a carriage 5 is held by the carriage shaft 3 and the guide portion 4 so as to be reciprocatingly movable along the shaft 3 and the guide portion 4. A motor (not shown) for driving the carriage 5 is mounted on the carriage 5, and a thermal head 6 capable of being brought close to and moved away from the platen 2 is attached to an end portion of the carriage 5 so as to face the platen 2.
A take-up bobbin 7 is provided on an upper surface of the carriage 5. An ink ribbon accommodated in an ink ribbon cassette (not shown) mounted on the carriage is wound around the take-up bobbin 7 while being guided between the platen 2 and the thermal head 6.
A paper insertion opening 8 for inserting paper sheets (not shown) into the body of the printer is formed at the rear of the platen 2. Feed rollers 9, which are rotated by a stepping motor (not shown) through a transmission mechanism to transport each paper sheet at a predetermined speed, are provided in the paper insertion opening 8. Pressure-contact rollers 10 are rotatably disposed below the feed rollers 9 and pressed against and maintained in contact with the same. Each paper sheet inserted into the nip between the feed rollers 9 and the pressure-contact rollers 10 through the paper inlet 8 is transported to a printing position by these rollers.
A printing mode select switch 12 is provided which is capable of selecting one of two printing modes: a first printing mode for printing by directly developing a color in heat-sensitive paper according to the kind of paper used, and a second printing mode for printing on plain paper by melting and transferring ink of the ink ribbon. A control unit (not shown) is also provided which controls the thermal printer according to the selection of the printing mode select switch 12.
The operation of this thermal printer will next be described.
In the thermal printer having the above-described construction, if printing paper used is heat-sensitive paper, the first printing mode is selected by the printing mode select switch 12 while the ribbon cassette is not mounted on the carriage 5. When a heat-sensitive paper sheet inserted through the paper insertion opening 8 is transported to the printing position, the thermal head 6 is pressed against the platen 2 only with the heat-sensitive paper interposed therebetween. In this state, a color is developed by selectively driving heating elements of the thermal head 6 while moving the carriage 5, thus performing printing.
If printing paper used is plain paper, the second printing mode is selected by the printing mode select switch 12. A printing paper sheet is inserted through the paper insertion opening 8 and is pinched between the feed rollers 9 and the pressure-contact rollers 10, and the feed rollers 9 are rotated to transport the printing paper in a direction perpendicular to the direction of movement of the carriage 5. When a printing start point on the printing paper reaches such a position as to face the platen 2, the rotation of the feed rollers 9 is stopped to stop transporting the printing paper. In this state, the thermal head 6 is pressed against the platen 2 at a predetermined contact pressure with the ink ribbon and the printing paper interposed therebetween, and the heating elements of the thermal head 6 are selectively driven on the basis of a printing signal while the carriage 5 is being moved. Simultaneously the take-up bobbin 7 is rotated to separate the ink ribbon from the printing paper after printing and to wind the separated ink ribbon around the bobbin 7. In this manner, desired is performed on the printing paper.
The above-described conventional thermal printer can print on heat-sensitive paper sheets or plain paper sheets fed one after another, but cannot perform multiple printing on a plurality of printing paper sheets superposed one on another. Accordingly, if a plurality of prints having the same content are required, it is necessary to repeat printing the same data for printing on a plurality of printing sheets or to perform printing in such a manner that a plurality of carriages are arranged in parallel with each other at predetermined intervals to print the same content of data on a corresponding row of the same number of printing sheets.
In the case where the same data is repeatedly printed on a plurality of printing sheets, there is a problem that a long time is taken to complete printing on the necessary number of printing sheets. In the case where a plurality of carriages are arranged in parallel with each other, there is a problem of the thermal printer being increased in its overall size.